The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
As problems of environmental pollution are getting more serious, use of non-polluting energy is becoming increasingly important. One of major causes of air pollution is exhaust gas from vehicles.
To mitigate such problems and to enhance fuel economy, environmentally-friendly vehicles (green cars) have been developed and used.
Recently, plug-in hybrid vehicles have been developed. The plug-in hybrid vehicle has a battery capacity greater than a conventional hybrid vehicle Also, the plug-in hybrid vehicle charges a battery using external electricity such that the vehicles run a short distance with an electric vehicle (EV) mode and run with a hybrid electric vehicle (HEV) mode when the battery is depleted.
The plug-in hybrid vehicle is driven by using both or either of an engine operated by petroleum and a drive motor in the same manner as a conventional hybrid vehicle. However, the plug-in hybrid vehicle has a high voltage battery that has a large capacity, which also allows to get charged by external electricity.
According to the plug-in hybrid vehicle, the engine is operated and a state of charge (SOC) of the high voltage battery is charged using remaining driving torque of the engine to increase a time which the vehicle runs with the EV mode.
If a forcible charging method is used in the plug-in hybrid vehicle, temperature of the drive motor rises due to current. In this case, the vehicle cannot run with the EV mode, but with power of the engine. Therefore, the merits of the green car may not be significant and fuel economy may also be lowered.